[Shotimes] Do Air Dams, Spoilers, and Wings Work?

[Koll]

The factory *should* have this information.  Whether they choose to share it
with the unwashed is another matter.

Spoilers, air dams and wing do work.  Too well for F1 - they've been banned.
At something like 120MPH they exert over 1G of force.  Above 120 MPH they
could drive upside down if the road twisted and elevated to allow for it.

THAT would be cool!

  Koll

----- Original Message -----
From: "Ron Porter" <ronporter@prodigy.net>
To: <shotimes@autox.team.net>
Sent: Saturday, April 12, 2003 10:14 AM
Subject: RE: [Shotimes] Do Air Dams, Spoilers, and Wings Work?


> In this case, I believe that he is referring to the "skateboard" spoiler
on
> the Gen 3, which supposedly has a real benefit at higher speeds.
>
> Ron Porter
>
> -----Original Message-----
> From: shotimes-admin@autox.team.net
> [mailto:shotimes-admin@autox.team.net]On Behalf Of James F. Ryan III
> Sent: Saturday, April 12, 2003 11:28 AM
> To: shotimes@autox.team.net
> Subject: [Shotimes] Do Air Dams, Spoilers, and Wings Work?
>
>
> Found this excellent article on one of my Fiero sites.  It's from Sept 98
> issue of Car and Driver.  It has excellent info AND mentions the SHO!!!
>
> Jim Ryan
> Wayne, NJ
> 91 Plus  all white/mocha with fiberglass hood, rod shifter, & rear
spoiler
>
> 255 Lph fuel pump, SHO Shop can & horn, 80mm MAF, S&B cone filter, SHO
Shop
> HiFlow Y-pipe & cat-back exhaust, SHO Shop LPM, SHO Shop underdrive
pulleys,
> SHO Shop HiRevs Jr clutch & steel billet LiteWeight flywheel, reinforced
> engine & trans mounts, SHO Shop TQ limiters, SHO NUT aluminum SFBs, FPS
96
> SHO front brakes, Carbotech F brake pads, Nooks full-body SFCs, Koni adj
> struts, SHO Shop linear springs, 24mm FSB, 26mm RSB, SHO Shop steel f&r
> STBs, Bridgestone Potenza RE-730 225/55-16, CATZ MSP fog lights, police
> grille
>
>
>
>   When we hear a posh English accent, we assume the speaker
> is intelligent. If we see food packaged in a green box labeled "Organic!"
we
> assume it is healthful. Similarly, when we see a skirtlike air dam on the
> front of a car, or a wing or spoiler on it's rear deck, we presume it's a
> performance car. But do these devices in fact have an aerodynamic effect
on
> production cars? Or are they no more functional then a vinyl roof? They
come
> in so many configurations and sizes, and on so many kinds of cars, that
it's
> easy to dismiss them as nothing more then eye candy. But that's not always
> warranted, as we shall see.
>   Aerodynamics is almost as much black art as it is science, and problems
> that crop up when air is forced around an object are not easy to fathom.
As
> a car speeds down the road, for example, it creates a moving obstruction
in
> the atmosphere. Stationary molecules of air must move up, down, or
sideways
> to flow around the car as it forges ahead. The air that ends up underneath
> the car can be trapped by the various mechanical bits protruding from a
> car's undercarriage and end up being dragged along by the moving car.
That's
> how a car can pick up a scrap of paper as it passes over it and whisk the
> paper along in its wake. Dragging this air along requires energy and
> comprises a large fraction of a car's aerodynamic drag.
>   Moreover, the flow of air underneath the car can build pressure at the
> front of the car and in the engine bay, lifting it upward, resulting in
less
> force pressing the tires to the pavement. That means less grip, which can
> adversely affect handling.
>   One way to attack these drag and lift problems is by creating a smooth
> underbelly. That can be done by installing panels underneath the car to
> reduce the likelihood of air being snagged and pressurized by underbody
> protrusions. But today, only pricey mid- and rear-engined production cars
> such as the Ferrari F355 and the Lotus Esprit use such panels because of
the
> cost of manufacturing and installing these parts, known as "belly pans."
>   A far more common solution is the front air dam, a rigid, skirtlike
panel
> that extends below the front bumper. This dam diverts air upward over the
> hood, or into a grille opening, or around the sides of the vehicle.
>   At the rear of the car, the goal is to keep the air flowing smoothly
over
> the body so that the hole the car punches through the atmosphere closes as
> neatly as possible. Airflow that closely follows the contour of the car is
> called "attached" or "laminar." The shape that best achieves this laminar
> flow is the teardrop---the configuration formed by a drop of rain as it
> falls through the air (round end first, for science philistines). GM's
> super-efficient EV1 electric car approximates this shape, but more
> conventional contours can also maintain laminar flow. The essential
contour
> is a rear window that is sloped to within 25 or so degrees of horizontal.
> Many hatchbacks are so designed, as are such cars as the Chevy Corvette
and
> the Toyota Supra.
>   But keeping the air attached to the vehicle can present a different set
of
> challenges. When you observe such a hatchback car from the side, it is
> curved on top and flat on the bottom---like the cross section of an
airplane
> wing. When air flows over a shape like this, the air must travel faster
over
> the top than over the bottom. This phenomenon produces lift and is known
as
> Bernoulli's principle, which maintains that a pressure drop must when
> airflow is accelerated. The pressure over the top of the car might be only
a
> fraction of a psi less than the pressure on the bottom, but that
difference
> acts over a large area of the car---from 10 to 20 square feet. The
pressure
> difference also increases with speed. Traveling at more then 100 mph in
some
> cars can produce hundreds of pounds of lift. Lift generated this way
> typically acts more on the rear of the car. But it has a similarly
> destabilizing effect on handling as front-end lift.
>   Vehicles with more-vertical rear windows---such as formal sedans,
wagons,
> and minivans---don't suffer from these lift problems as much, because the
> air spills behind their more-upright rear windows in randomly tumbling
eddy
> currents. This is what's known as turbulence, and although it limits lift,
> it's a major contributor to drag.
>   The middle ground between these two conditions---between 28 and 32
degrees
> of backlight angle---is no solution, either. At this angle, the air can't
> decide whether it should stay attached or become turbulent, so it does
both
> unpredictably. Aerodynamicists  are about as fond of this backlight angle
as
> they are of a vertical, flat windshield.
>   Rear wings and spoilers were invented to address these lift and airflow
> issues. Wings come in many shapes and sizes, but they share a common
> characteristic---a narrow, horizontal surface, mounted away from the body
in
> clean, undisturbed air. (Wings mounted close to the body are either
> nonfunctional or act more like spoilers, described below.) Wings add
> downforce---the opposite of lift. One way to create downforce is to shape
> the wing into an airfoil---an airplane wing of sorts---and turn it upside
> down. This forces the flow below the wing to travel at a higher velocity
> then the air above, creating a downward force. A second way to create such
> downforce is to angle the front of the wing slightly downward into the
> airflow. This creates more drag then a horizontal airfoil, but it can
allow
> adjustability of the downforce.
>   To differentiate a spoiler from a wing, think of turkey plumage. The
> spoiler is an angular, liplike appendage attached to, or designed into,
the
> rear of the car. It can be used to create downforce like a wing , but it's
> more commonly used to reduce lift or drag. On hatchbacks, a lip spoiler
can
> create a pool of air ahead of the spoiler that separates the airflow from
> the backlight, reducing lift. It can also be used at the rear of the car
to
> launch the airflow cleanly away from the vehicle, preventing its tendency
to
> remain attached to the car's trailing surfaces. This can decrease drag as
> well as reduce the underbody pressure that contributes to lift.
>   Automakers were hard at work on drag reduction as far back as the 1930s.
> It wasn't until the early 1960s, as both race-car and production-car top
> speeds approached 200 mph, that lift became an issue. Ferrari racer Richie
> Ginther is credited with inventing the rear spoiler for downforce in 1961,
> and discreet rear spoilers started appearing on competition Ferraris soon
> thereafter. One of the first cars to use a front air dam was Ford's GT40.
> The high snouts of early prototypes produced so much lift at 200 mph that
> they were virtually undrivable. Fitting a air dam increased the force on
the
> front-tire contact patches from 310 pounds to 604 pounds at top speed. The
> Dodge Charger Daytona and Plymouth Superbird twins of 1969-70 were among
the
>
> first production cars to sport a rear wing. The adjustable wing, supported
> high above the rear deck by finlike butresses, combined with changes to
the
> nose of the car (including an air dam) to increase downforce at both ends
of
> the car. This allowed test drivers to lap Daytona speedway 5 mph faster.
>   Porsche was probably more responsible then any other carmaker for
turning
> air dams and spoilers into fashion statements. The 1975 Turbo's integrated
> front air dam and huge whale-tail spoiler in back cut overall lift on the
> cantankerously handling 911 by a whopping 90 percent. The
> air-dam-and-plumage look soon became synonymous with the prestigious
Porsche
> brand. By the late 1970s, just about any car aspiring to a performance
image
> wore some kind of air dam or spoiler.
>   Today, air dams, spoilers, and wings can be found on such supercars as
the
> Dodge Viper GTS and Acura NSX, where you would expect them. But they also
> adorn the exteriors of Dodge Neons, Toyota Corollas, Oldsmobile Intrigues,
> and other sedans, many of which are not capable of speeds of much more
than
> 100 mph.
>   Which raises an important point; these aerodynamic devices don't do much
> if your not going fast. Aerodynamic drag doesn't even exceed tire drag
until
> you've reached 40 to 50 mph, and you may have to be doing well over 100
mph
> for spoilers and wings to have any appreciable effect on lift or
downforce.
> This is because aerodynamic forces vary with the square of a car from 80
to
> 160 mph, and if faces a four-fold increase in lift and drag forces.
>   Nearly all cars can benefit from the drag-reducing effects of an
air-dam.
> The Pontiac Grand Prix sedan's front air dam, for example, reduces that
> car's overall drag by 5 to 10 percent. Front air dams also help with
engine
> cooling and can even serve as a useful place to mount fog lights.
>   Carmakers don't deny, though, that rear wings and spoilers are often
more
> show than go. At GM, spoilers are usually added as a marketing-driven item
> at the beginning of a car's development, according to John Plonka, an
> aerodynamics-development engineer at the company. "From there, we take
those
> pieces and try to make them aerodynamically useful, with varying success,"
> he adds. John Doughty, chief designer of Ford's Advanced Design Studio,
> describes a similar story but adds that "if we found that it detracted
from
> the performance, we wouldn't recommend it." Perhaps such a recommendation
> was made, but not heeded, on the Ford Mustang Cobra.
>   Some carmakers would rather not install spoilers but offer them simply
> because car buyers demand them. "Personally, it hurts to see a Camry with
a
> [nonfunctioning] spoiler on the back," says Donald W. Brown, former
national
> product-planning manager for Toyota in the U.S., "but if the dealers are
> going to put them on anyway, we would rather supply them to ensure their
> compatibility with the car."
>   That doesn't mean these devices are never beneficial to workaday cars.
> Brown notes that the factory rear spoiler on the Lexus SC trims its
> coefficient drag from 0.32 to 0.31, and Ford's Doughty notes a similar
> improvement with the rear wing of the Ford Taurus SHO. A future Ford
economy
> car might end up with a rear spoiler solely for fuel-economy reasons, says
> Doughty.
>   So, it appears  that front air dams are usually functional, whereas rear
> wings and spoilers are as often functional as they are frivolous. Ford
> Advanced Studio designer Grant Garrison sums it up this way: "If wings and
> spoilers weren't popular, we wouldn't put them on cars. We'd find some
other
> way to make them aerodynamic."
>   In other words, if wings and spoilers are what car buyers want, that's
> what they'll get. Whether they work or not.
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